Risk Assessment of Radon in Drinking Water (1999) / Chapter Skim
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2 Baseline Information on Indoor Radon and Radon in Water in the United States
2 Baseline Information on Indoor Radon and Radon in Water in the United States
Pages 32-49
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From page 32... ...
Although it is not possible to accurately predict radon concentrations in individual houses because of the highly variable nature of factors that control radon entry and concentrations in a specific house, one can estimate the distribution of indoor radon concentrations on a regional basis. Several approaches have been taken to develop indoor-radon potential maps of the United States, and succeeding studies have built on previous ones; the most recent maps of predicted indoor radon encompass a statistical analysis of variables that account for the greatest variation in indoor radon: geology, climate, and house structure.
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From page 33... ...
~ _/ 1 /f4~ ~ COASTAI PLA t1~ Limit of Glaciation FIGURE 2.1 Geologic-physiographic map of the United States (courtesy of USGS)
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From page 35... ...
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From page 36... ...
The principal geologic sources of radon in the United States are: · Uranium-bearing metamorphosed rocks, volcanics, and granite intrusive rocks that can be highly deformed or sheared (shear zones in these rocks cause the largest indoor-radon problems in the United States) , found predominantly in the Appalachian Mountains, Rocky Mountains, and Basin and Range; · Glacial deposits derived from uranium-bearing rocks and sediments found in the northern tier of states above the limit of glaciation; · Marine black shales found in the Appalachian Plateau and Great Plains and to a smaller extent in the Coastal Plain, Colorado Plateau, and Basin and Range; · High-iron soils derived from carbonate, especially in karstic terrain found in the Appalachian Plateau, Appalachian Mountains, and Coastal Plain; and · Uranium-bearing fluvial, deltaic, marine, and lacustrine deposits and phosphatic deposits found in the Colorado Plateau, Rocky Mountains, Great Plains, Coastal Plain, Basin and Range, and Appalachian Plateau.
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From page 37... ...
The New England states overall had the highest radon concentrations in water from all sources; state geometric means ranged from 18,500 Bq m-3 in Massachusetts to 88,800 Bq m-3 in Rhode Island. A population-weighted geometric mean for the United States of 6,900 Bq m-3 was reported.
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From page 38... ...
reviewed available studies of outdoor radon from around the world and observed consistent diurnal and seasonal trends. Generally, the diurnal pattern of outdoor radon concentration includes early morning and evening maxima related to cooling and air stability.
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From page 39... ...
The ratio of maximums to minimums generally ranges from 1.5 to 4. Seasonally in the United States, maximum outdoor radon concentrations often occur in the summer to early winter and minimum concentrations in the late winter to spring in reaction to meteorologic changes and moisture conditions in the ground.
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From page 40... ...
There has been only one national study in the United States, but several ambient-radon studies have been carried out on the state or regional scale or at a single site over
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From page 41... ...
National Studies In the late 1980s, EPA conducted a national survey of ambient radon across the United States (Hopper and others 1991) to confirm previously reported concentrations and in response to section 302 of the Indoor Radon Abatement Act, which stated that "the national long-term goal of the United States with respect to radon levels in buildings is that the air within buildings in the United States should be as free of radon as the ambient air outside of buildings." Section 303 also required EPA to include information regarding outdoor ambient radon concentrations around the country in the updated Citizens Guide to Radon.
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From page 43... ...
BASELINE INFORMATION ON INDOOR RADON AND RADON IN WATER IN THE U.S. 43 Quarter 6 Quarter 7 Quarter 8 Quarter 9 Fall Winter Spring Sum.
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From page 44... ...
The authors (Hopper and others 1991) emphasize that the study does not statistically represent the distribution of ambient radon concentrations in the United States but indicates that estimates of annual average ambient radon concentrations and the associated error estimates can be derived for each site.
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From page 45... ...
The range and values of concentrations were generally very similar to what Hopper and others found for the United States. As part of a statewide radon study, indoor radon was measured at 300 sites throughout California (Liu and others 1991~.
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From page 46... ...
Monthly average outdoor radon concentrations were higher during the colder months of the year, however it is the daily variations of the outdoor radon that account for the variation by a factor of 2 in radon concentration. A site in Central Park, New York was also monitored for outdoor radon over a 3-y period using a passive alpha-track detector; they found an average of 7 Bq m-3 and trends similar to those in their northern New Jersey study (N.
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From page 47... ...
2-filter Central Park, 3 y 7.0 Etched track N Harley NY (personal communication)
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From page 48... ...
The ambientradon data of Hopper and others (1991) are the only data that provide some portion of national coverage over an extended period, but the committee has concerns about the appropriateness of using these data to develop a populationweighted average for the United States.
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From page 49... ...
A comprehensive, geographically based ambient-radon study that incorporates the major population areas of the United States and their geologic variability would provide the basis for a valid population-weighted ambient radon concentration. Focused regional studies of ambient radon in high-radon areas such as the glaciated northern tier of states and states of the Appalachian Mountains, Rocky Mountains, and Basin and Range would yield better information on overall exposure and morerealistic baseline information for evaluating the contribution of the ambient concentration to what is observed in indoor air.
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